A new plant attributed to Cladoxylopsida from the Middle Devonian of Yunnan Province, China

Abstract

A new plant is described on the basis of compression fossils from the Xichong Formation, Middle Devonian (upper Givetian) of Yunnan Province, China. The plant has a stout stem (up to 90 mm diameter). Lateral sterile branches are ramified in a series of perpendicular dichotomies (proximally close and ‘digitate’), terminating in recurved tips, and lack appendages. Fertile branches are unramified, and have fertile appendages attached in a helical pattern. The fertile appendages are composed of a central axis to which is attached proximally a pair of sporangia, and which distally becomes flattened or broadened with a shallow terminal dissection and two pairs of sporangia attached on each side of the dissection in a fan-like arrangement. Sterile and fertile branching systems are not found in organic connection, but are inferred to belong to the same plant both because of close association and because both sterile branching systems and fertile appendages bear characteristic narrow spines. Although the affinities of this plant are not certain, we assign it to Cladoxylopsida on the basis of the ‘digitate’ branching from which we infer an underlying highly dissected vascular system. However the plant lacks many characteristics of the best defined group of Middle Devonian Cladoxylopsida, Pseudosporochnales, including sterile appendages, straight tips and distinctive sclerid nests within the cortex. After consideration, previous records of Pseudosporochnus in South China are discounted as the digitate branches featured probably represent our new plant. The new plant, named Rhipidophyton acanthum Berry et Wang gen. et sp. nov, further highlights the phytogeographic isolation of the Yunnan Middle Devonian flora, and suggests greater diversity of Middle Devonian cladoxylopsid bauplans than previously recognised.